Solutions and Colligative Properties
Solutions Solution = Solute + Solvent Concentration Composition of Solutions 'Mass Percentage' Mass % = M1 / M2 x 100 'Volume Percentage' Volume % = V1 / V2 x 100 Mass/Volume Percentage M/V % = Mass of solute (gm) / Volume of Solution (mL) It is the strength of the Solution PPM Parts per million = (Mass of Solute / Mass of Solution ) x 100 'Grams per Litre' 'Molarity' Molarity = No. of Moles of Solute / Volume of Solution (L) = n / V Molarity changes with change in temperature and pressure , because Volume changes with these parameters . For dilution ; M1V1 = M2V2 NOTE : MV = no. of moles For mixing ; MRVT = M1V1 + M2V2 + M3V3 .......+ MnVn Demal Unit A demal unit is number of moles of solution one litre of solution at 0o C Molality Molality = No. of Moles of Solute / Mass of Solution (kg) = n / m Molality remains constant with change in temperature and pressure , because number of moles and mass does not change with these parameters . 'Formality' Formality is the number of gram formula weights per litre of solution . 'Normality' Normality is the number of equivalents present in one litre of solution . Normality = of Solute) / (Equivalent weight of Solute x Volume of Solution ) N1V1 = N2V2 'Mole Fraction' Mole Fraction = No. of Moles of Solute / No. of moles of Solution Note that is a fraction and not a percentage . Solvation The process of particles of a solvent surrounding the solute is called as Solvation . The process of ionization by a solvent is called as Solvolysis . If the solvent is water it is called as Hydrolysis . Solvolyis occurs only if the Solvent is polar . Water is a polar molecule ; that is why it can ionize NaCl . Solubility of Gases in Liquids Effect of temperature : Inversely Proportional . Because as temperature increases , the volume of gas increases more than that of liquid due to which the liquid becomes inadequate for solvation . Effect of Pressure : Directly Proportional . Volume Increases with decrease in Pressure . Effect of addition of soluble salt : The soluble salt will displace the gas to get dissolved . The gas will be released from the liquid with formation of bubbles . Colligative Properties Lowering of Vapour Pressure Vapour Pressure : '''Vapour pressure is the amount of pressure exerted by the vapour of a liquid on the surface of the liquid , when it is in equilibrium . '''Vapour Pressure lowering : '''Vapour Pressure can be lowered by adding non-volatile solute in a solution . ' '''Relative lowering of Vapour Pressure' Determination of Molecular Weights Raoult's Law for non-volatile solution : Po- P1 / Po = x2 Molar mass and relative lowering of vapour pressure Boiling Point Elevation Boiling Point is the temperature at which the vapour pressure of the liquid becomes equal to the vapour pressure of the atmosphere . Boiling Point can be increased by increasing the external pressure . Freezing Point Depression Freezing point is the temperature at which the vapour pressure of liquid becomes equal to the vapour pressure of solid . Freezing Point Depression is directly proportional to Vapour pressure lowering and molality . Osmosis The semi-permeable membrane allows solvent particles to pass but not the solute particles . The spontaneous and unidirectional flow of solvent molecules through a semi-permeable membrane into the solution is called Osmosis . The solvent molecules move from a solution of lower concentration to higher concentration through the semi-permeable membrane . Osmotic Pressure The excess of pressure on the side of solution that stops the net flow of solvent into solution through semipermeable membrane is called osmotic pressure . Two or more solutions having the same osmotic pressure are called as isotonic solutions . A solution having osmotic pressure higher than that of other solution , then i is called as hypertonic with that solution . A solution having osmotic pressure lower than that of another solution is said to be hypotonic with that solution . Van't-Hoff - Boyle's Law At constant temperature , the osmotic pressure (π) of a dilute solution is directly proportional to the Molar concentration and inversely proportional to the volume of the solution . π α C / V Van't Hoff - Charle's Law At constant concentration , the osmotic pressure of a dilute solution is directly proportional to the absolute temperature . π α T Van't Hoff' General Solution Equation π α T/V π = CRT Vant Hoff Factor Category:Chemistry